1. Field of the Invention
The present invention relates to a hub unit to which a wheel and a disc rotor of a disc brake apparatus are mounted and other vehicle-use bearing apparatuses. More particularly the present invention relates to a vehicle-use bearing apparatus provided with a double row rolling bearing with vertex of contact angles outside of bearing on an outer periphery of a hub wheel.
2. Description of the Related Art
In a conventional vehicle-use bearing apparatus a cylindrical recessed portion is formed at an axial end of a hub wheel. The portion is bent and deformed radially outward and caulked onto an outer end face of an inner ring of a rolling bearing by using a rolling caulking jig to thereby prevent the rolling bearing from coming off the hub wheel and to apply pre-load to the rolling bearing.
The hub wheel is formed by using steel material such as JIS (Japanese Industrial Standards) S40C to S58C and SUJ2, for example. Such material includes sulfur for convenience in turning and in order to obtain stability of quality. For example, a percentage of sulfur content in steel material is specified to be 0.035% by weight or less when the steel material of JIS S40C to S58C is used as the steel material for the hub wheel and a percentage of sulfur content in steel material is specified to be 0.025% or less when the steel material of SUJ2 is used respectively in terms of convenience in turning and stability of quality for the steel material.
The present inventors found that a minute crack occurred in the caulked portion when rolling caulking was carried out and pursued study of it. As a result, because a percentage of sulfur content in the steel material to be used was set at an upper limit value or a value approaching the upper limit value in order to further improve a turning property and stability of quality, manganese sulfide was liable to be generated in the steel material by chemical combination of sulfur with manganese included in the steel material. The manganese sulfide which is a nonmetallic inclusion generated in the steel material became a starting point of a crack in the rolling caulking. Then, the inventor further pursued study and found a percentage of sulfur content with which the crack could be suppressed.